Method of heat-treating additively manufactured ferromagnetic components

ABSTRACT

A method of heat-treating an additively-manufactured ferromagnetic component is presented and a related ferromagnetic component is presented. A saturation flux density of a heat-treated ferromagnetic component is greater than a saturation flux density of an as-formed ferromagnetic component. The heat-treated ferromagnetic component is further characterized by a plurality of grains such that at least 25% of the plurality of grains have a median grain size less than 10 microns and 25% of the plurality of grains have a median grain size greater than 25 microns.

BACKGROUND

Embodiments of the disclosure generally relate toadditively-manufactured ferromagnetic components. More particularly,embodiments of the disclosure relate to a method of heat-treatingadditively-manufactured ferromagnetic components.

In electrical machines, ferromagnetic components channel magnetic flux.Typical methods of forming ferromagnetic components of an electricalmachine, involve multiple steps and multiple parts that are assembledtogether. Use of multiple steps and multiple parts results in cumbersomemanufacturing processes, and may also affect the machine's endperformance and reliability. Furthermore, in some topologies, theferromagnetic components may be structured as insulated laminascompacted together to form a core of the ferromagnetic component.Lamination and insulation may minimize losses such as eddy currentlosses which may otherwise represent a significant part of energy lossin an electrical machine. However, limitations on the sizes of steelsheets from which laminas are constructed may pose difficulties inassembling multiple laminated components together to form a singlecomponent. More complex topologies may decrease losses, increasemagnetic flux density, or both, but are difficult to manufacture withconventional methodologies.

Additive manufacturing techniques may be employed to fabricate bothlaminated and unlaminated ferromagnetic components of an electricalmachine. However, additively-manufactured ferromagnetic components maynot provide the desired ferromagnetic properties for the end-useapplication. Thus, there is a need for improved methods of manufacturingadditively-manufactured ferromagnetic components for electricalmachines.

BRIEF DESCRIPTION

In one aspect, the disclosure relates to a method of heat-treating anadditively-manufactured ferromagnetic component such that a saturationflux density of a heat-treated ferromagnetic component is greater than asaturation flux density of an as-formed ferromagnetic component. Theheat-treated ferromagnetic component is further characterized by aplurality of grains such that at least 25% of the plurality of grainshave a median grain size less than 10 microns and 25% of the pluralityof grains have a median grain size greater than 25 microns.

In another aspect, the disclosure relates to a ferromagnetic component,including a plurality of grains such that at least 25% of the pluralityof grains have a median grain size less than 10 microns and 25% of theplurality of grains have a median grain size greater than 25 microns.The ferromagnetic component has a unitary structure and a saturationflux density greater than 2 Tesla.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings,wherein:

FIG. 1 illustrates a schematic drawing of an additive manufacturingsystem for manufacturing an additively-manufactured ferromagneticcomponent, in accordance with some embodiments of the disclosure;

FIG. 2A shows a solid cylindrical ferromagnetic component manufacturedusing an additive manufacturing technique, in accordance with someembodiments of the disclosure;

FIG. 2B shows a solid ring ferromagnetic component manufactured using anadditive manufacturing technique, in accordance with some embodiments ofthe disclosure;

FIG. 2C shows a helical spring ferromagnetic component manufacturedusing an additive manufacturing technique, in accordance with someembodiments of the disclosure;

FIG. 3 illustrates a perspective view of an engine coupled to agenerator that includes a ferromagnetic component, in accordance withsome embodiments of the disclosure;

FIG. 4 shows the direct current (DC) magnetization curves forcommercially available heat-treated Vacoflux 50 sample (ComparativeSample 1), as-formed additively-manufactured cylindrical sample(Comparative Sample 2), and heat-treated additively-manufacturedcylindrical sample (Sample 2);

FIG. 5 shows the relative permeability curves for commercially availableheat-treated Vacoflux 50 sample (Comparative Sample 1), as-formedadditively-manufactured cylindrical sample (Comparative Sample 2), andheat-treated additively-manufactured cylindrical sample (Sample 2); and

FIG. 6 shows the static hysteresis loops shape for as-formedadditively-manufactured cylindrical sample (Comparative Sample 2) andheat-treated additively-manufactured cylindrical sample (Sample 2).

DETAILED DESCRIPTION

In the following specification and the claims, which follow, referencewill be made to a number of terms, which shall be defined to have thefollowing meanings. The singular forms “a”, “an” and “the” includeplural referents unless the context clearly dictates otherwise. As usedherein, the term “or” is not meant to be exclusive and refers to atleast one of the referenced components being present and includesinstances in which a combination of the referenced components may bepresent, unless the context clearly dictates otherwise.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value solidified by aterm or terms, such as “about”, and “substantially” is not to be limitedto the precise value specified. In some instances, the approximatinglanguage may correspond to the precision of an instrument for measuringthe value. Similarly, “free” may be used in combination with a term, andmay include an insubstantial number, or trace amounts, while still beingconsidered free of the solidified term. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged, such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

Solidified microstructures obtained using laser-based additivemanufacturing techniques are an example of materials science atextreme—with over million Kelvin per second solidification rates,ultra-fine microstructures, and far-from-equilibrium meta-stable phaseformation. Therefore, the microstructures obtained, using typicaladditive manufacturing techniques, in ferromagnetic materials,especially, grain size, phase stability and grain texture, are nottailored for direct electromagnetic (EM) applications, due to highhysteresis losses.

Embodiments of the present disclosure address the noted shortcomings inthe art. Inventors of the present application have unexpectedly found aheat-treatment procedure that provides a surprising ability to improvethe magnetic properties of additively-manufactured ferromagneticcomponents to substantially match the magnetic properties ofcommercially-produced wrought components. These magnetic properties areattained despite a marked difference in microstructure between theadditively-manufactured and wrought components.

In some embodiments, a method of heat-treating anadditively-manufactured ferromagnetic component is presented such that asaturation flux density of a heat-treated ferromagnetic component isgreater than a saturation flux density of an as-formed ferromagneticcomponent. The heat-treated ferromagnetic component is furthercharacterized by a plurality of grains such that at least 25% of theplurality of grains have a median grain size less than 10 microns and25% of the plurality of grains have a median grain size greater than 25microns.

An additively-manufactured ferromagnetic component, in accordance withthe embodiments described herein, is manufactured using an additivemanufacturing technique. “Additive manufacturing” is a term used hereinto describe a process which involves layer-by-layer construction oradditive fabrication (as opposed to material removal as withconventional machining processes). Such processes may also be referredto as “rapid manufacturing processes”. The additive manufacturingprocess forms net or near-net shape structures through sequentially andrepeatedly depositing and joining material layers. As used herein theterm “near-net shape” means that the additively manufactured structureis formed very close to the final shape of the structure, not requiringsignificant traditional mechanical finishing techniques, such asmachining or grinding following the additive manufacturing process. Incertain embodiments, suitable additive manufacturing processes include,but are not limited to, the processes known to those of ordinary skillin the art as direct metal laser melting (DMLM), direct metal lasersintering (DMLS), direct metal laser deposition (DMLD), laser engineerednet shaping (LENS), selective laser sintering (SLS), selective lasermelting (SLM), electron beam melting (EBM), fused deposition modeling(FDM), or combinations thereof. These methods may employ, for example,and without limitation, all forms of electromagnetic radiation, heating,sintering, melting, curing, binding, consolidating, pressing, embedding,and combinations thereof.

The additive manufacturing processes in accordance with embodiments ofthe disclosure may be used on suitable metallic materials, e.g., metalalloys, to form the ferromagnetic components of the electrical machine.In some embodiments, the ferromagnetic component includes a soft metalalloy. In some embodiments, the soft metal alloy includes iron andcobalt. In some embodiments, the soft metal alloy further includessilicon, vanadium, or a combination thereof. These materials may be usedin these methods and systems in a variety of forms, as appropriate, fora given material and method, including, for example, without limitation,granules, powders, sheets, foils, tapes, filaments, pellets, wires, andcombinations of these forms.

FIG. 1 illustrates a schematic drawing of an additive manufacturingsystem 100 used for manufacturing an additively-manufacturedferromagnetic component, in accordance with embodiments of thedisclosure. Only some components of an additive manufacturing system 100are shown in FIG. 1 for purposes of simplicity but it would beunderstood that other components, may also be included. In FIG. 1, anenergy source 110 directs an energy beam 101 towards portions of asurface of a bed 120 of a ferromagnetic material. Non-limiting examplesof suitable energy beam include laser, electron beam, or a combinationthereof. The energy beam 101 fuses a portion of the ferromagneticmaterial together, whereupon the bed 120 of the ferromagnetic materialis lowered in the direction 121 and a fresh layer of ferromagneticmaterial is deposited thereupon by a suitable applicator 130 (e.g., aroller or a swiping blade). This is typically referred to as one “buildstep” of an additive manufacturing process. The terms “fuse” or “fusing”as used herein refer to agglomeration, melting, sintering a portion ofthe ferromagnetic material to each other, as well as to a portion orportions of underlying ferromagnetic material (if present). By applyingsuccessive steps of fusing and depositing, a three-dimensional component140 is manufactured.

In this example, the three-dimensional component 140 is illustrated ashelical in shape, however, any other three-dimensional topology suitableas a ferromagnetic component is also encompassed within the scope of thedisclosure. Non-limiting examples of other three-dimensional topologiesof the ferromagnetic components envisaged within the scope of thedisclosure includes rings, cylinders, spirals, and the like. Further,the methods as described herein may be suitable for laminated as well asnon-laminated ferromagnetic components. FIG. 2A shows a solidcylindrical ferromagnetic component 140 manufactured using an additivemanufacturing technique, in accordance with some embodiments of thedisclosure. FIG. 2B shows a solid ring ferromagnetic component 140,manufactured using an additive manufacturing technique, in accordancewith some embodiments of the disclosure. FIG. 2C shows a helical springferromagnetic component manufactured using an additive manufacturingtechnique, in accordance with some embodiments of the disclosure.

In some embodiments, the method in accordance with embodiments of thedisclosure further includes providing an additively-manufacturedferromagnetic component, before the heat-treatment step. The term“providing” as used herein includes embodiments wherein theadditively-manufactured ferromagnetic component is procured from asuitable source, as well as embodiments wherein theadditively-manufactured ferromagnetic component is manufactured, forexample, using a technique described in FIG. 1, before theheat-treatment step. Further, the term “additively-manufacturedferromagnetic component” as used herein refers to the final componentformed after the additive manufacturing process as well as to theintermediate layers or sub-components formed during the additivemanufacturing process. For the sake of brevity, the terms“additively-manufactured ferromagnetic component” and “ferromagneticcomponent” are used herein interchangeably.

Furthermore, the term “as-formed ferromagnetic component” refers to anadditively-manufactured ferromagnetic component that has not besubjected to an additional heat-treatment step besides the fusing stepsemployed during the additive manufacturing technique, as describedhereinabove. Therefore, while referring to FIG. 1, the component 140 maybe referred to an “as-formed ferromagnetic component” if it hasn't beensubjected to an additional heat-treatment step either during, or, afterthe additive manufacturing process used to form the component. The term“heat-treated ferromagnetic component” refers to anadditively-manufactured ferromagnetic component that has been subjectedto at least one additional heat treatment step during, or, after thecompletion of the additive manufacturing process. The component 140,after being subjected to one or more additional heat-treatment steps(during, or, after the additive manufacturing process) may be referredto as a “heat-treated ferromagnetic component.”

In accordance with embodiments of the disclosure, “heat-treating” or“heat-treatment step” refers to holding the ferromagnetic component at atemperature greater than the ferrite-to-austenite transitiontemperature, for at least 10 min. The heat-treatment may be implementedas isothermal heat treatment, i.e., the ferromagnetic component issubjected to a substantially constant temperature for a certain periodof time, or, alternatively, as a cyclic heat treatment wherein theferromagnetic component is subjected a particular temperature for aparticular duration of time, cooled, and then heated again. In someembodiments, the ferromagnetic component is heat treated at atemperature in a range from about 900° C. to about 1200° C. In certainembodiments, the ferromagnetic component is heat treated at atemperature in a range from about 1020° C. to about 1100° C. Further,the heat-treatment is implemented for a time duration in a range fromabout 1 hour to about 4 hours. In certain embodiments, theheat-treatment is implemented as an isothermal heat treatment at 1100°C. for a time duration of 4 hours.

As noted earlier, inventors of the present application have surprisinglyfound that after heat-treating the ferromagnetic component at elevatedtemperatures, although the median grain-size of the grains in theferromagnetic component increased, there was a wide distribution ingrain sizes, with clusters of both small and large grain sizes. The widedistribution in grain sizes is unlike the typical grain distributionseen in commercially-available heat-treated wrought ferromagneticcomponents. Despite, the differences in microstructure of theheat-treated ferromagnetic components of the present disclosure and thecommercially available wrought components, the heat-treatedferromagnetic components unexpectedly showed improved ferromagneticproperties similar to those of the commercially available wroughtcomponents.

In some embodiments, the as-formed ferromagnetic component has a mediangrain size less than or equal to 10 microns and the heat-treatedferromagnetic component has a median grain size greater than or equal to20 microns. In some embodiments, the as-formed ferromagnetic componenthas a median grain size less than or equal to 5 microns and theheat-treated ferromagnetic component has a median grain size greaterthan or equal to 50 microns.

The distribution in grain sizes in the heat-treatedadditively-manufactured ferromagnetic component can be furthercharacterized by the number fraction of the grains that are smaller thana first grain size and the number fraction of the grains that are largerthan a second grain size. As mentioned previously, the heat-treatedferromagnetic component is characterized by a plurality of grains suchthat at least 25% of the plurality of grains have a median grain sizeless than 10 microns and 25% of the plurality of grains have a mediangrain size greater than 25 microns. In some embodiments, at least 25% ofthe plurality of grains have a median grain size less than 10 micronsand at least 50% of the plurality of grains have a median grain sizegreater than 25 microns.

The heat-treated ferromagnetic component may be further characterized bya median grain size. In some embodiments, the heat-treated ferromagneticcomponent has a median grain size in a range from about 10 microns toabout 50 microns. In certain embodiments, the heat-treated ferromagneticcomponent has a median grain size in a range from about 10 microns toabout 25 microns.

As noted earlier, the saturation flux density of the heat-treatedferromagnetic component is greater a saturation flux density of anas-formed ferromagnetic component. A saturation flux density of anas-formed ferromagnetic component may be, for example, equal to or lessthan 1.6 Tesla, and the saturation flux density of the heat-treatedferromagnetic component may be greater than 1.6 Tesla. In someembodiments, the saturation flux density of the heat-treatedferromagnetic component is greater than 2 Tesla. In certain embodiments,the saturation flux density of the heat-treated ferromagnetic componentis greater than 2.3 Tesla. Heat-treatment of the additively-manufacturedferromagnetic component, in accordance with embodiments of thedisclosure, further exhibited increase in saturated relativepermeability. In some embodiments, the unsaturated relative permeabilityof the heat-treated ferromagnetic component is greater than 2000. Incertain embodiments, the unsaturated relative permeability of theheat-treated ferromagnetic component is greater than 2500. Theheat-treated ferromagnetic components further showed reduction inhysteresis curve area leading to a reduction in hysteresis losses whichis reflected in lower specific iron losses [W/kg] at the lower frequencyrange (hysteresis loss˜frequency).

The heat-treatment may be implemented during, or, after the additivemanufacturing process. In some embodiments, the heat treatment isperformed after the additive manufacturing process. Thus, in suchembodiments, while referring to FIG. 1, the additively-manufacturedferromagnetic component 140 is further subjected to one or moreheat-treatment steps, as described earlier, to form a heat-treatedferromagnetic component 150.

In some other embodiments, the heat treatment is performed during atleast one build step of an additive manufacturing process used to formthe additively-manufactured ferromagnetic component. In some suchinstances, with continued reference to FIG. 1, the heat treatment may beperformed using the same directed energy source 110 used during thebuild step of the additive manufacturing process. This may be applicableto any additive modality that uses directed energy, including lasermelting/sintering and electron beam melting. Further, in such instances,the heat-treatment may be performed using for example a beam splittingtechnique and/or by modulating the power of the directed energy source,during a particular build step. For example, during a build step, afterthe ferromagnetic material has fused with itself and with underlyinglayers (if present), the power of the energy source (e.g., laser) may bemodulated such that the build layer is heat treated at a desiredtemperature for a particular time duration. In some such embodiments,the heat treatment may be performed, after each build step, such thatsubsequent build layers of the ferromagnetic component 140 are heattreated individually. In some other embodiments, the heat treatment maybe performed after the last build layer is formed and during the finalbuild step for manufacturing the ferromagnetic component 140.

The methods of heat treating, in accordance with embodiments of thedisclosure, cover uniform heat treatment for an entire additivelymanufactured ferromagnetic component, as well as non-uniform heattreatment. In some embodiments, different portions of the ferromagneticcomponent may be selectively heat treated to achieve determinedsaturation flux density and tensile strength values in these portions.The selective heat treatment of ferromagnetic component may beimplemented during, or, after the additive manufacturing process. By wayof example, in instances where stator laminations integrated withhousing/cooling jackets are additively manufactured, only the fluxcarrying components may be selectively heat treated. Similarly, ininstances where a rotor core is additively manufactured with anintegrated shaft, only the flux carrying components (i.e., theferromagnetic components) may be selectively heat treated.

Thus, in accordance with some embodiments of the disclosure, the heattreatment processes as described herein may enable: 1) annealing offerromagnetic components in-situ, i.e., during the build and/or 2)locally tailoring the magnetic properties by locally controlling theheat treatment during the build. In some embodiments, this may furtherprovide an additive-enabled part count reduction and more cost-effectiveelectric machines used in hybrid electric propulsion.

The method may further include the step of incorporating theheat-treated ferromagnetic component into an electrical machine.Non-limiting examples of suitable electrical machines include a motor, agenerator, a transformer, a toroid, an inductor, and combinationsthereof. In certain embodiments, an electric machine refers to anelectric motor that converts electric power to mechanical power or to anelectric generator that converts mechanical power to electric power. Theelectrical machine in accordance with embodiments of the disclosure mayhave any suitable topology, for example, a radial, an axial, or atransverse flux topology.

FIG. 3 is a perspective view of an embodiment of an electric machine 200(e.g., electric generator 200) coupled to an engine 300 (e.g., an engineof an automobile or an aircraft). While the illustrated electric machine200 is an electric generator, it may be appreciated that the methodsdiscussed herein are applicable to other electric machines, such aselectric motors. In the illustrated embodiment, the electric generator200 may be described relative to an axial direction 14, a radialdirection 16, and a circumferential direction or an annular direction18. The electric generator 200 includes a rotor assembly 220 and astator assembly 240. The rotor assembly 220 is configured to rotate inthe circumferential direction 10 relative to the stator assembly 240.The rotational energy (e.g., the relative rotation between the rotorassembly 220 and the stator assembly 240) is converted to electricalcurrent in armature or power generation coil within the stator or rotorassembly, depending on the design of the electric generator 200.

The rotor assembly 220 includes a rotor core 222 and is mounted on ashaft 227 such that the rotor core 222 rotates together with the shaft227. The stator assembly 240 also includes a stator core 242. Further,the rotor assembly 220 and the stator assembly 240 generally bothinclude coil windings. In certain embodiments, the rotor assembly 220includes field windings that generate a magnetic field, and the statorassembly 240 includes armature or power generation windings thatgenerate electrical power as the rotor assembly 220 rotates. In otherembodiments, the stator assembly 240 may include field windings, androtor assembly 220 may include the armature or power generationwindings. In some embodiments, the rotor core 222 includes theheat-treated ferromagnetic component 150, as described herein.

In some embodiments, a ferromagnetic component is also presented. Theferromagnetic component includes a plurality of grains such that atleast 25% of the plurality of grains have a median grain size less than10 microns and 25% of the plurality of grains have a median grain sizegreater than 25 microns, wherein the ferromagnetic component has aunitary structure and a saturation flux density greater than 2 Tesla.

The term “unitary structure” as used herein refers to a structurewherein all of the structural features of such structure are integralwith each other. As used herein, the term “integral” means that thedifferent geometric and structural features that define the unitarystructure are formed together as features of a single, continuous,undivided structure, as opposed to previously formed or otherwisemanufactured components that are assembled together or otherwise joinedor affixed together using one or more of various joining means to yielda final assembled product. Thus, the different stnictural or geometricfeatures of the unitary structure are not attached to or affixed to eachother, e.g., bolted to, welded to, brazed to, bonded to, or the like. Aunitary structure in accordance with the embodiments described hereinmay be formed using an additive manufacturing technique, described indetail earlier.

In some embodiments, the ferromagnetic component includes a soft metalalloy. In some embodiments, the soft metal alloy includes iron andcobalt. In some embodiments, the soft metal alloy further includessilicon, vanadium, or a combination thereof. The ferromagnetic componentmay be further characterized by a median grain size. In someembodiments, the ferromagnetic component has a median grain size in arange from about 10 microns to about 50 microns. In certain embodiments,the heat-treated ferromagnetic component has a median grain size in arange from about 10 microns to about 25 microns.

In some embodiments, an electrical machine including the ferromagneticcomponent is also present. FIG. 3 depicts an example of an electricalmachine 200 including a heat-treated ferromagnetic component 150, inaccordance with embodiments of the disclosure.

Additive manufacturing of ferromagnetic components of electricalmachines can enable circumventing complex assemblies of electricalcomponents by building complex near-net-shape geometries, such asmanufacturing of radial, axial and transverse flux laminatedferromagnetic parts. Additional benefits include thermal management viaincorporating intricate cooling channels, weight reduction due to theability to manufacture intricate details that are not possible withconventional machining/subtractive processes. Additive manufacturingmight also allow reducing the number of parts in an electric machine byeliminating connection components (such as bolts, rivets, brackets etc.)and/or eliminating joining processes (such as brazing, soldering, gluingetc.). Further, additive manufacturing of electric machine componentsmay enable dramatic reductions in cycle time for development; and.manufacturing costs may be reduced by avoiding the need for expensivetooling and iterative modification of the tooling. However, as mentionedearlier, the microstructure, especially, grain size, phase stability andgrain texture, of additively-manufactured ferromagnetic components isnot tailored for direct electromagnetic (EM) applications due to highhysteresis losses.

By employing heat-treatment procedures on additively-manufacturedferromagnetic components, in accordance with embodiments of thedisclosure, the required combination of ferromagnetic properties suchas, higher saturation flux density, higher relative permeability, andlower hysteresis losses may be attained.

Further, locally heat treating the ferromagnetic material during theadditive manufacturing process offers the machine designer theflexibility to effectively tailor the material performance to meet bothmagnetic and mechanical performance requirements. For example, regionsof the ferromagnetic component subjected to high mechanical stress, butlow magnetic flux change, could be locally heat treated to have hightensile strength. Regions that are mechanically static but have highfrequency flux change could thus be heat treated to have low losses. Thecapability provided by some of the embodiments of the disclosure maytherefore open up the design space to include machine topologies withboth high-power density and high efficiency. The benefits may accrue tothe balance of systems in the product, such as simpler thermalmanagement systems and lighter structural support members.

Examples

The powder material for the additive manufacturing process was suppliedby Sandvik Osprey Ltd. (Neath, UK). The chemistry of the alloy was50Fe-49.9Co-0.1Si (wt % nominal) and 49.5Fe-50.49Co-0.01Si (wt %actual), and the powder size was −53 μm+15 μm (96.4%). The powder wasused to build spiral laminates using laser-based additive manufacturingtechnique, as shown in the FIGS. 1 and 2C. The spiral laminates had anouter diameter of 50 mm, an inner diameter of 43 mm, and had 18 layers,each 0.47 mm thick. Additionally, two other solid samples weremanufactured using additive manufacturing, as shown in FIG. 2A (solidcylinder sample) and FIG. 2B (solid ring sample). The solid ring sampleshad an outer diameter of 50 mm, an inner diameter of 43 mm, and wasabout 6.3 mm thick. The solid cylindrical samples had the dimensions of92 mm×10 mm. All samples were manufactured on EOS machines by CitimGmbH, Barleben, Germany. The solid cylinder samples were used for DCtests, and the solid ring samples and the laminated spiral samples forAC tests. All electromagnetic tests were conducted using a REMAGRAPH®C—500 at Magnet-Physik, Köln, Germany.

A commercially available FeCo alloy (Vacoflux 50, commercially availablefrom VACUUMSCHMELZE GmbH & Co. KG, Hanau, Germany) was used as acomparative example. The alloy was rolled into a sheet and heat treatedat 850° C. for 1 hour. This heat-treated sample was used as ComparativeSample 1. Additively-manufactured FeCoSi cylindrical samples that werenot subjected to any heat-treatment were used as Comparative Sample 2.Additively-manufactured FeCoSi helical spring samples that were notsubjected to any heat-treatment were used as Comparative Sample 3.

Samples measuring 5 mm×5 mm were cut from the additively-manufacturedspiral samples for heat treatment. The additively-manufactured solidring and cylindrical samples were heat-treated as such. All the sampleswere heat-treated in vacuum or argon-2.9% hydrogen forming gas in afurnace with heating elements. The additively-manufactured spring andcylindrical samples were heat-treated at 750° C. and 850° C. for 4hours. These heat-treated cylindrical samples were used as ComparativeSample 4 and the heat-treated spring samples were used as ComparativeSample 5. The additively-manufactured spring and cylindrical sampleswere also heat-treated at higher temperatures in the range from 1025° C.to 1100° C. for a time duration in a range of 2 to 4 hours. The heattreatment was either isothermal or cyclic. For cyclic heat-treatment, a3-cycle ‘cyclic’ heat-treatment between 900° C. and 1025° C. with 5 minat each temperature and heating/cooling rates of 5° C./min was employed.The additively-manufactured spring samples that were isothermallyheat-treated at 1100° C. for 4 hours were used as Sample 1. Theadditively-manufactured cylindrical samples that were isothermallyheat-treated at 1100° C. for 4 hours were used as Sample 2. Table 1provides the component characteristics and heat treatment conditions fordifferent samples described herein.

TABLE 1 Component characteristics and heat treatment conditions fordifferent samples Component Heat Heat treatment Sample Characteristicstreated conditions Comparative Commercially available Yes Isothermalheat Sample 1 Vacoflux 50 FeCo alloy treatment at rolled into a sheet850° C. for 1 hour Comparative Additively-manufactured No Sample 2FeCoSi cylindrical sample Comparative Additively-manufactured No Sample3 FeCoSi spring sample Comparative Additively-manufactured YesIsothermal heat Sample 4 FeCoSi cylindrical sample treatment at 850° C.for 4 hours Comparative Additively-manufactured Yes Isothermal heatSample 5 FeCoSi spring sample treatment at 850° C. for 4 hours Sample 1Additively-manufactured Yes Isothermal heat FeCoSi spring sampletreatment at 1100° C. for 4 hours Sample 2 Additively-manufactured YesIsothermal heat FeCoSi cylindrical sample treatment at 1100° C. for 4hours

Post heat-treatment, the samples were sectioned and metallographicallypolished for microstructure characterization. Microstructurecharacterization was conducted using scanning electron microscopy (SEM),transmission electron microscopy (TEM), and electron backscatterdetector analysis (EBED).

SEM micrographs for the heat-treated rolled sheet of Vacoflux 50(Comparative Sample 1) showed a more uniform grain structure with mediangrain size in the range of 50-100 μm. SEM micrographs of as-formedadditively-manufactured cylindrical samples (Comparative Sample 2) andadditively-manufactured spring samples (Comparative Sample 3) showedelongation of grains. Nearly bi-modal distribution (small and largegrain clusters) were also observed, although the microstructure waslargely equiaxed. The median grain size was less than 5-10 μm. Evenafter heat-treating the additively-manufactured samples at 850° C. for 4hours (Comparative Samples 4 and 5), no significant increase in thegrain size was observed. However, heat-treating theadditively-manufactured samples at 1100° C. for 4 hours (Samples 1 and2), led to significant recrystallization and grain growth in they-austenite phase. The heat treatment temperature of 1100° C. wassignificantly higher than the ferrite-to-austenite transitiontemperature. However, in contrast to Comparative Sample 1, a widevariation in grain size population was observed in Sample 1, whichincluded a larger fraction of large-grains and a small fraction ofsmall-grain clusters. While the median grain size was still below 50 μm,a good fraction of the sample did exhibit larger grains with grain sizebetween 50-100 μm.

The magnetic properties for the samples prepared in accordance withembodiments of the disclosure as well as for the comparative sampleswere also measured. FIG. 4 shows the direct current (DC) magnetizationcurves, also referred to as DC BH curves, where B represents the fluxdensity in Tesla and H represents magnetic field strength in kA/m. FIG.4 shows the DC BH curves for commercial available heat-treated Vacoflux50 sample (Comparative Sample 1), as-formed additively-manufacturedcylindrical sample (Comparative Sample 2), and heat-treatedadditively-manufactured cylindrical sample (Sample 2). As shown in FIG.4, the saturation flux density of the additively-manufacturedcylindrical sample increased from 1.6 Tesla (Comparative Sample 2) to2.35 Tesla (Sample 2), after the heat treatment. Further, the saturationflux density (BH) curve of the additively-manufactured cylindricalsample (Sample 2) almost matched that of heat-treated non-additivelymanufactured Vacoflux 50 (Comparative Sample 1).

FIG. 5 shows the relative permeability curves for commercial availableheat-treated Vacoflux 50 sample (Comparative Sample 1), as-formedadditively-manufactured cylindrical sample (Comparative Sample 2), andheat-treated additively-manufactured cylindrical sample (Sample 2). Asshown in FIG. 5, the unsaturated relative permeability of theadditively-manufactured cylindrical sample increased from 700(Comparative Sample 2) to 2600 (Sample 2), after the heat treatment.Further, the relative permeability curve of the additively-manufacturedcylindrical sample (Sample 2) almost matched that of heat-treatednon-additively manufactured Vacoflux 50 (Comparative Sample 1).

FIG. 6 shows the static hysteresis loop shapes for as-formedadditively-manufactured cylindrical sample (Comparative Sample 2) andheat-treated additively-manufactured cylindrical sample (Sample 2). Thecomparison of the curves indicates a reduction in hysteresis loop areafor Sample 2 leading to a reduction in hysteresis losses, which isreflected in lower specific iron losses [W/kg] at the lower frequencyrange (hysteresis loss ˜frequency). Similar results were also observedfor the ring and helical spring samples.

Thus, inventors of the present application have unexpectedly found aheat-treatment procedure that results in improvement in ferromagneticproperties despite the formation of an irregular microstructure.

The appended claims are intended to claim the invention as broadly as ithas been conceived and the examples herein presented are illustrative ofselected embodiments from a manifold of all possible embodiments.Accordingly, it is the Applicants' intention that the appended claimsare not to be limited by the choice of examples utilized to illustratefeatures of the present disclosure. As used in the claims, the word“comprises” and its grammatical variants logically also subtend andinclude phrases of varying and differing extent such as for example, butnot limited thereto, “consisting essentially of” and “consisting of.”Where necessary, ranges have been supplied; those ranges are inclusiveof all sub-ranges there between. It is to be expected that variations inthese ranges will suggest themselves to a practitioner having ordinaryskill in the art and where not already dedicated to the public, thosevariations should where possible be construed to be covered by theappended claims. It is also anticipated that advances in science andtechnology will make equivalents and substitutions possible that are notnow contemplated by reason of the imprecision of language and thesevariations should also be construed where possible to be covered by theappended claims.

The invention claimed is:
 1. A method, comprising: heat-treating anadditively manufactured ferromagnetic component such that a saturationflux density of a heat-treated ferromagnetic component is greater than asaturation flux density of an as-formed ferromagnetic component, whereinthe heat-treated ferromagnetic component is further characterized by aplurality of grains such that at least 25% of the plurality of grainshave a median grain size less than 10 microns and 25% of the pluralityof grains have a median grain size greater than 25 microns.
 2. Themethod of claim 1, wherein the additively manufactured ferromagneticcomponent comprises a metal alloy comprising iron and cobalt.
 3. Themethod of claim 2, wherein the metal alloy further comprises silicon,vanadium, or a combination thereof.
 4. The method of claim 1, whereinthe saturation flux density of the heat- treated ferromagnetic componentis greater than 2 Tesla.
 5. The method of claim 1, wherein anunsaturated relative permeability of the heat-treated ferromagneticcomponent is greater than
 2500. 6. The method of claim 1, wherein theas-formed ferromagnetic component has a median grain size less than orequal to about 5 microns and the heat-treated ferromagnetic componenthas a median grain size greater than or equal to about 20 microns. 7.The method of claim 1, wherein the heat-treated ferromagnetic componenthas a median grain size in a range from about 10 microns to about 25microns.
 8. The method of claim 1, wherein the additively manufacturedferromagnetic component is heat treated at a temperature in a range from900° C. to about 1200° C.
 9. The method of claim 1, whereinheat-treating is performed during at least one build step of an additivemanufacturing process used to form the additively manufacturedferromagnetic component, wherein a directed energy source is used duringthe at least one build step of the additive manufacturing process. 10.The method of claim 9, wherein heat-treating is performed using the samedirected energy source used during the at least one build step of theadditive manufacturing process.
 11. The method of claim 1, whereindifferent portions of the additively manufactured ferromagneticcomponent are selectively heat treated to achieve determined saturationflux density and tensile strength values in these portions.
 12. Themethod of claim 1, wherein the additively manufactured ferromagneticcomponent is at least a portion of an electrical machine component. 13.A method, comprising: heat-treating an additively manufacturedferromagnetic component such that a saturation flux density of aheat-treated ferromagnetic component is greater than a saturation fluxdensity of an as-formed ferromagnetic component, wherein theheat-treated ferromagnetic component is further characterized by aplurality of grains such that at least 25% of the plurality of grainshave a median grain size less than 10 microns and 25% of the pluralityof grains have a median grain size greater than 25 microns, whereindifferent portions of the additively manufactured ferromagneticcomponent are selectively heat treated to achieve determined saturationflux density and tensile strength values in these portions, wherein theheat-treating includes holding the additively manufactured ferromagneticcomponent at a temperature greater than a ferrite-to-austenitetransition temperature for at least 10 min.
 14. The method of claim 13,wherein the heat-treating is performed during at least one build step ofan additive manufacturing process used to form the additivelymanufactured ferromagnetic component, wherein a directed energy sourceis used during the at least one build step of the additive manufacturingprocess.
 15. The method of claim 14, wherein the heat-treating isperformed using the same directed energy source used during the at leastone build step of the additive manufacturing process.
 16. The method ofclaim 13, wherein the saturation flux density of the heat-treatedferromagnetic component is greater than 2 Tesla.
 17. A method,comprising: heat-treating an additively manufactured ferromagneticcomponent such that a saturation flux density of a heat-treatedferromagnetic component is greater than a saturation flux density of anas-formed ferromagnetic component, wherein the heat-treatedferromagnetic component is further characterized by a plurality ofgrains such that at least 25% of the plurality of grains have a mediangrain size less than 10 microns and 25% of the plurality of grains havea median grain size greater than 25 microns, wherein the heat-treatedferromagnetic component has a unitary structure and a saturation fluxdensity greater than 2 Tesla, wherein the heat-treating includes holdingthe additively manufactured ferromagnetic component at a temperaturegreater than a ferrite-to-austenite transition temperature, for at least10 min.
 18. The method of claim 17, wherein an unsaturated relativepermeability of the heat-treated ferromagnetic component is greater than2500.
 19. The method of claim 17, wherein the additively manufacturedferromagnetic component comprises a metal alloy comprising iron andcobalt.
 20. The method of claim 19, wherein the metal alloy furthercomprises silicon, vanadium, or a combination thereof.